Answer: A U.S. Provisional Application is a patent application that may be filed in the U.S. only, but which will never mature into a patent.  If no PCT (i.e. international application) or parallel applications are filed within 12 months of the filing date, the application is abandoned, unpublished.  The application should include a full disclosure of the invention, but no claims or drawings are necessary.  Most importantly, the official filing fees are less than those for a regular U.S. application. 

All this sounds nice, especially the fact that it seems like the costs are less.  But are they really?  The question remains: Should I file a provisional application?